Shale retorting process



Jan. 2, 1968 R. F. DEI-:RING

SHADE RETORTING PROCESS Filed May 13, 1965 NQ Pm INVEN TOR. @OLA/V0 E' DEER/M6 BY ZWM 5 xmy United States Patent Office 3,361,644 Patented Jan. 2, 1968 3,361,644 SHALE RETQRTING PROCESS Roland F. Deering, La Habra, Calif., assignor to Union Gil Company of Caiifornia, Los Angeies, Calif., a corporation of Caiifornia Filed May 13, 1965, Ser. No. 470,281 The portion of the term of the patent subsequent to Dec. 27, 1977, has been disclaimed 11 Claims. (Cl. 20L-29) This application is a continuation-impart of my copending application of Ser. No. 13,508 led Mar. 8, 1960, and now abandoned, Which -in turn is a continuation-inpart of Ser. No. 589,272, filed June 4, 1956, and issued as U.S. Patent 2,966,446 on Dec. 27, 1960. This invention relates generally to a process for the continuous treatment of oil-containing or oil-producing solids `for the extraction of gas and liquid products therefrom. More particularly, this invention relates to a new and improved process for the retorting of oil shale to recover optimum hydrocarbon oil and gas values therefrom.

The essential feature of my invention entails an oil shale retorting process wherein eduction is accomplished by recycling a pre-heated portion of the rich product shale shale `gas to la solidsupflow, fluid-downflow retort, and wherein the eduction fluid is indirectly heated to retorting temperatures and is maintained essentially oxygen-free throughout the process.

Some processes for the eduction of shale oils and gases involve the downward passage of shale rock as a moving bed by gravity through a vertical heat treating kiln. During this passage they are heated to eduction temperatures by direct or indirect means. From a thermal efliciency standpoint the direct heating means is preferred in which a countercurrent contact of hot gases with the shale rock is employed. To avoid the large fuel consumption otherwise required, most of these processes involve the direct injection of lair or other oxygen-containing gas into the bottom of the kiln to burn the carbonaceous residue from the spent shale. This generates hot Aline gases needed to heat the rock. However, diiculties are encountered with the fusion of the spent shale due to this burning, and frequently the fused or partially fused rock plugs the air inlet, requiring a shutdown. Since all of the hydrocarbon product is removed at the top of the kiln, in most processes it must `oe -removed as a vapor and this requires extensive cooling and condensing facilities. In the rest of these processes the oil is condensed as a mist and is carried out by the gas stream. However this also causes frequent operating diiculties because of agglomeration and run-back of the oil into the kiln where it is decomposed or otherwise lost.

Other shale eduction processes have successfully avoided the large fuel and condensing water requirements and the diiliculties resulting from refluxing or runback of oil by utilizing an upow of shale rock and a downflow of heating gas. The shale is fed upwardly successively through a perforated disengaging section and a heat treating or kiln section. Air or other oxygen-containing gas enters the top and moves downwardly through the heat treating section, is first preheated in cooling the hot shale ash at the top, burns the carbonaceous residue from the spent shale at la lower level, and the ho-t ilue gases continue downwardly to still lower levels where they heat the shale rock and educt hydrocarbon oils and gases. The whole vapor phase passes downwardly in direct contact with the raw shale, and is cooled, thereby condensing the hydrocarbon oil and preheating the raw shale near the bottom of the kiln section. The liquid and gaseous products are drawn oif at the disengaging section and are thus separated from the upwardly moving shale rock. A solids feeder passes the shale rock upwardly through the disengaging and heat treating sections and displaces the shale ash out the top of the unit. The process supplies its own fuel in the 'form of carbonaceous spent shale. It cools and partially condenses its own product in preheating the raw shale rock.

Several problems however are involved in the latter upfiow solids process which are occasionally troublesome. Because the process derives its heat from the burning of a solid hydrocarbonaceous residue on the educted or retorted solids by contacting it with an oxygen-containing gas, the burning temperatures are necessarily of the order of l,800 F. to 2,500 F. inside the apparatus and the shale feed Vrate is limited by the rate at which this residue can be burned. With some oil-producing solids, specilically Colorado oil shale, as much as 30 percent to 60 percent of the heat so generated is consumed in uselessly decomposing the mineral carbonates, c g., calcium carbonate to calcium oxide (li-me) and carbon dioxide. These high temperatures also result in incipient fusion of the shale ash causing the forma-tion of clinkers or partially sintered agglomerates which adversely .affect 4the upow of solids as well as the ow of gas down through the retort. One way of solving these problems is to employ some means for agitating the burning solids so as to prevent formation of these agglomerates or -break up those which do form. In the past this agitation has ybeen accomplished -by plows which rotate through the top of the upwardly moving solids bed. Because of the high temperatures and the high stresses involved, these plows require large quantities of power to move them, are necessarily constructed of alloy steel with rather elaborate supporting and rotating structures, and must be cooled to prevent high temperature failure.

An additional problem involves the presence of oxygen in the system to support the combustion of the carbonaceous residue on the spent shale. Unavoidably, a part of this oxygen reacts with the educted materials to form partially oxidized materials which apparently render the liquid portion of the product yrather unstable, with resulting fouling of processing apparatus and formation of gums, sludges, etc. A Ifurther problem arises in the disposal of the tremendous quantities of low B.t.u. waste product gas which result from combustion retorting. Combustion retorting product gas is not a particularly satisfactory fuel product because it is diluted with large amounts of ue gases. This low B.t.u. waste gas can usually ybe burned in special burners adapted to the combustion of llow heating value gas. However this waste product gas is not economically transportable since flue gas dilution requires the handling of large quantities of inert gases. Furthermore, there is a substantial loss of naphtha or light ends in combustion retorting. These gasoline range materials, carried out with the immense volumes of waste product gas, are substantially unrecoverable as liquid fuel products.

It is therefore among the objects of this invention to provide an improved oil shale retorting process which successfully overcomes these and other problems and which achieves high oil recovery, yields a high B.t.u. product gas, minimizes degradation of the liquid product, and produces an oil product of substantially increased stability and quality having an increased naphtha and decreased residuum content, when compared with oil from combustion retorting.

It is a particular object of this invention. to provide an oil shale eduction process wherein the optimum conditions of eduction can be more selectively and independently controlled, resulting in an increased oil yield. More specifically, in the eduction zone of the retort, conditions such as recycle eduction liuid volume, temperature, composition `and the like, are correlated and independently controlled for best overall results, rather than as dictated by the requirements of another process zone, eg., the generation in a burning zone of an eduction flue gas as in combustion retorting A further object of t-his invention is to provide an oil shale retorting process wherein high eduction rates and high heating rates in the kiln can be realized, along with complete elimination of oxygen from the eduction system, thus avoiding liquid product degradation.

A more particular object of this invention is to provide an oil shale eduction process wherein the entire retort height is devoted to retorting the solids and cooling and condensing the products, with no structural height being necessary to provide a separate zone for burning of the spent shale, as in combustion retorts.

A still further object of this invention is to provide a retorting process wherein thermal eiciency is substantially increased, as compared to typical combustion gas retorts, through a reduction in the maximum kiln operating temperature to one at which only a minor proportion of the naturally occurring mineral carbonates are decomposed. Other objects and advantages of this invention will become apparent to those skilled in the art as the description and illustration thereof proceed.

I have now found that the foregoing objects canV be realized in a hot product gas recirculation retorting process. More particularly, the novel recycle gas retorting process of this invention embraces a substantially continuous upward feed of oil shale particles of up to about 6 inches, preferably in the size range of 1/8 inch to 2 inches, in a vertical retort, the kiln section of which typically has a horizontally enlarging area with increase in elevation. The retort is enclosed so as to exclude air or any oxygen-containing gas from the interior, and from contact with the educted products. Shale is fed typically by a vertically acting piston feeder located within a feeder case below the kiln, and can be of the form shown in U.S. Patent No. 2,501,153, to Berg, or any satisfactory for-m which provides uniform solids upow within the retort. Shale particles, having had the optimum oil quantity educted therefrom are removed from the top of the eduction zone. These spent shale particles are found to be substantially unchanged in exterior physical size and configuration throughout the retorting process. Product gases, vapors, and liquids, along with the eduction fluid, are removed just above the bottom entry location of the fresh shale feed, and an indirectly heated recycle stream of hot shale product gas is continuously supplied to the top ofthe eduction zone.

The hot product recycle eduction gas, preferably at about 1,000 F. to 1,300 F., and less than about 1,500" F. maximum temperature, passes downwardly into and through the upward flow of shale. This hot eduction gas is generally effectively supplied at a superficial mass velocity of about 100 to about 800 pounds per hour per square foot of bed cross section at the surface of the eduction zone. These gas fow rates are particularly applicable to oil shale having a Fischer assay range of about 80 gallons per ton to as low as 10 gallons per ton or lower. The eduction zone temperatures required for the proper eduction of shale in the recycle gas retort of this invention are usually between about 600 F. and about 1,200 F., and preferably between about 800 F. and 1,000 F., depending upon the type of shale being retorted and the products desired. A preferred minimum eduction zone temperature is that temperature at which the shale product gas make is a quantity at least sufficient to provide, when burned, all the heat necessary to raise the eduction fluid stream to the required retorting temperature. Hence, at those preferred eduction temperatures, extraneous fuel gas is not required. The highest temperatures exist at the top of the kiln, and decrease down through the eduction zone until the lowest eduction temperature is found adjacent the shale preheating zone. Shale in the eduction zone need not, and preferably does not, exceed about 950 F. These lower temperatures substantially limit carbonate decomposition while still providing complete hydrocarbon eduction. While the eduction zone pressure is usually near atmospheric, the pressures can be either subatrnospheric of superatmospheric, with the pressure at the top of the eduction zone always being higher than the pressure in the lower zones.

The eduction gas, being a recycled shale product gas, contains essentially no free oxygen with which educted oil can combine chemically, nor does it contain many of the conventional diluents found in ue gases such as nitrogen, argon, etc. This product gas, collected with the liquid shale oil product in an accumulation reservoir, is usually withdrawn at a temperature of between about F. and about 200 F., preferably at about 150 F., and consists mainly of hydrogen and light hydrocarbons, e.g., methane, et-hane, propane and the like.

The improved process of this invention may be more readily understood with reference to the accompanying drawing-which is an elevational view in partial crosssection of the major items of the equipment employed, and includes a schematic ow diagram of the process. For simplicity and ease of understanding, the conventional associated equipment such as liquid oil pumping means, ow controlling means, valves, pumps, recycle lines, heat exchangers, and the like, have for the most part not been illustrated, since conventional apparatus can be used and forms no part of the invention.

Referring now more particularly to the drawing, the process of the present invention will be described yin terms of a specic example as applied to the retorting of oil shale of 0 to 6 inches in average size, and at a rate of 700 tons per day. The apparatus consists essentially of three parts; namely, an upper heat treating or eduction kiln 10 about 14 feet high and averaging 15 feet in diameter, an intermediate perforate disengaging section 12 about 11 feet high and having upper and lower diameters of about 13 feet and 5.5 feet, respectively, and a lower reciprocating piston shale feeder contained within feeder housing 14.

Shale feeder housing 14 contains a vertically reciprocating feeder piston 16 which is 5.5 feet in diameter and is contained within feeder cylinder 18. Cylinder 18 oscillates in a vertical plane about trunnion 20 so that it may be moved between the vertical feeding position shown and an inclined cylinder charging position, not shown, in which the upper outlet opening of cylinder 18 is disposed to the left and immediately below the lower outlet opening of shale feed hopper 21. A yhydraulic actuating cylinder 22 disposed within cylinder 18 reciprocates feeder piston 16 in cylinder 13 vertically a distance of about 2.0 feet. A second hydraulic cylinder 24 contained within feeder case 14 oscillates feeder cylinder 18 between the lling and feeding positions. A V-shaped trough 15 runs along the bottom of the case and has a screw conveyor at its lower apex to move settled fines toward outlet 19. A stream of product oil from line 61 is introduced by pump 72 into case 14 through line 23 controlled by valve 25 and serves to ush the fines slurry from outlet 19 through line 27. This slurry is returned to settler 60 by pump 29 and line 31 at a rate controlled by valve 33 to settle the recycle fines.

Raw shale is introduced by any convenient conveyor means, not shown, in the direction indicated into feed hopper 21 at a rate of 700 tons per day. With feeder piston 16 disposed at its upper extremity immediately after its upstroke, cylinder 18 is moved to a point in alignment with feed hopper 21. Cylinder 22 retracts piston 16 drawing a charge of shale rock into the upper part of feeder cylinder 18. Hydraulic cylinder 24 is then extended returning feeder cylinderp18 to the vertical position shown. Then hydraulic cylinder 22 is extended forcing piston 16 upwardly thereby moving the charge of rock `into disengaging section 12 and displacing the rock therein and in kiln 10 upwardly. This cycle is repeated,

thereby continuously feeding fresh shale at the bottom of the structure and displacing hot spent shale from the top.

The educted shale is displaced by rotating rakes or scrapers SS from the top of kiln inside housing 26.`

Rakes 58 can also be reciprocating devices. The spent shale falls by gravity through the paths indicated by arrows 28 and 29 downwardly onto the bottom 30 of housing 26 and discharges through outlet 32 into spent shale cooling and second recycle gas preheating zone 34. Here the spent shale passes downwardly as a dense moving bed countercurrently to a rising stream of the second recycle gas produced as hereafter described and introduced to ring manifold 46. This gas is introduced at a temperature of about 160 F. and is preheated by direct contact with the cooling spent shale to a temperature of about 850 F. The spent shale is simultaneously cooled from a ternperature of about 950 F. to about 450 F. The spent shale forms solids level 48 -in the upper portion of cooling zone 34 which is detected by means of solid level controller 50, which in turn controls the rate of discharged cooled spent shale from the bottom of cooler 34 by means of solids ow controller 52. The latter may be a valve or a star feeder or a vane feeder, the solids discharge rate of which is equal that at which spent shale discharges from the top of kiln 10 so as to maintain an approximately constant solids level 48. The spent shale is discharged through outlet line S4 onto spent shale disposal conveyor 56 and is removed from the system at a rate of about 581 tons per day.

The preheated second recycle gas stream is passed upwardly through outlet 32 into housing 26 wherein it directly mixes with the first recycle gas stream introduced thereto through line 44. This mixture forms the hot eduction gas which heats the upwardly moving shale and educts the oil and gas therefrom.

The raw shale is passed by means described above upwardly to perforated disengaging section 12 in which the cooled eduction and shale gases and the condensed shale oil are disengaged from the upwardly moving shale mass. In kiln 10 the upwardly moving shale passes successively through a fresh shale preheating and product cooling and condensing zone, and a preheated-shale eduction zone. These two zones occupy kiln 10 from top to bottom. The spent shale, expelled at the top of kiln 10, is moved radially by means of rotating rakes 58 which maintain a substantially iiat solids surface at the top of kiln 10 and which introduce the spent shale at a more or less constant rate through housing 26 and outlet 32 into Spent shale cooler 34. This spent shale is removed from the system as previously described and simultaneously preheats the second recycle gas stream.

The hot eduction gases produced pass downwardly rst through the shale eduction zone and then through the shale preheating and product cooling and condensing zone in kiln 10. This mixture of eduction gases and educted uids passes downwardly into disengaging zone 12 which is surrounded by an integrally attached product settling and separating zone 60. Disengaging zone 12 is provided with a plurality of apertures 62 opening into separator settler zone 60. Through these apertures the condensed liquid product flows, forming a body of liquid having level 64. The gas ows therethrough into the top part of separator settler 60 above the liquid level. The net liquid product is removed by means of line 66 at a rate controlled by valve 68 in accordance with liquid level controller 70 and is passed as a product of the process through line 74 to further processing or storage facilities not shown. Part of the liquid oil produced is recirculated from settler 60 through line 61 as previously described into feeder case 14 by means of pump 72. For the feed rate of about 700 tons per day of Colorado oil shale, whose Fischer assay is about 28 gallons per ton, the liquid product ow rate through line 74 is about 450 barrels per day of about 21.0 degree API gravity oil, corresponding to a retorting efliciency of about 96 percent.

The gas phase is withdrawn from separator settler 60 through line 76 under the inuence of recycle gas blower 78 and is drawn through one or more mist separators indicated generally at 80. This separator may comprise a cyclone separator, an oil wash such as in an oil absorber, or an electrostatic precipitator, or any other suitable separators or combinations thereof for removing finely divided liquid particles from a gas stream. Any recovered liquid is removed via line 81 and is combined with the product liquid flowing through line 74.

The t-hus treated gas stream is pumped by blower 78 through line 82 at a rate controlled by valve 84 in accordance with flow recorder controller 86. This gas contains about 7 percent carbon monoxide, about 18 percent hydrogen, and about 58 percent hydrocarbon on a dry basis and has a gross heating value of about 1,000 B.t.u. per standard cubic foot. A first portion of this shale product -gas is passed from line 82 through line 110, line 88, and line 132 at a rate controlled by valve 133 into coil 130 located in gas burning zone 94. The recycled shale gas introduced through line 132 passes through gas -heating coil 130 and is thence passed to the top of the retort via line and hot recycle gas line 44 as the lirst recycle gas stream. Gas burning zone 94 is maintained at appropriate temperatures for heating the recycle gas stream to retorting temperatures by combustion of either product gas introduced via lines S8 and 126 into gas burning zone 94 at a rate controlled by valve 12S, or by means of an auxiliary fuel gas introduced to line 126 via line 140 at a rate controlled by valve 142. Suiicient air, which can be preheated, is introduced through line 96 at a rate controlled by valve 98. This fuel gas and air generate hot flue gases in burning zone 94 which pass upwardly on the [outside of coil 130. The tlow of flue gas and shale gas being heated can be made concurrent or countercurrent in burner 94 by suitable connections to coil 130. The hot ue gases are passed to a stack through line 134. It is to be understood that any substantially equivalent form of indirect heating is satisfactory for raising the eduction Huid to retorting temperatures.

The rst recycle gas stream can be tempered Iby mixing the hot gases flowing through line 100 with portions of cool shale gas flowing through line 104 at a rate controlled by valve 106 in response to the temperature of the first recycle gas stream as detected by temperature recorder controller 108. Preferably the blend is controlled so ias to maintain the first recycle gas stream at a temperature of between about l,000 F. and about 1,500 F. This iirst recycle gas stream ows through line 44 into the top of housing 26 in which it is mixed with the second recycle gas stream which was preheated in spent shale cooler 34. This mixture is the eduction gas stream which heats the shale and educts further quantities of shale oil and gas therefrom. It flows downwardly through the rising shale bed at a rate of about 24,000 M. s.c.f./d.

The aforementioned second recycle gas `stream is pumped by means of blower 78 through line S2 into line 110 at a rate controlled by valve 112 and pressure recorder controller 114 which measures the gas pressure existing at the bottom of spent shale cooler 34. By this means a gas flow is maintained up through cooler 34 of sutlicient magnitude to generate the pressure differential therein which is equal to that existing between the top of kiln 10 and apertures 62 in disengaging section 12 thus preventing the entry of atmospheric air into the system through cool ash outlet 54. The kiln thus operates at slightly below atmospheric pressure Ibecause hopper 21 having oil level 64 is open to the air. However with a slight and obvious modification the process and apparatus can be operated at superatmospheric pressures as well.

The net shale gas product is discharged through line 116 at a rate of about 550 M s.c.f./d., controlled by valve 118 and pressure recorder controller 120, if none of the shale gas product is used as fuel in burner 94.

However, as much as 60 percent or more of this net shale gas product can be required for heating in burner 94. This net shale product gas is particularly desirable in that the gross heating value exceeds S Btu/scf., and usually is about 1060 B.t.u./s.c.f. Because of its high heating Value, the net shale product gas is suitable for commercial distribution, requiring only conventional pretreating steps.

In one modification of my invention, the second recycle stream is blocked off by closing valve 112 and the entire recycled shale product gas is passed through coil 134) to raise this stream to eduction temperatures as previously described. In this modification, steam or other seal gas is introduced into the lower portion of spent shale cooler 34 through line 144 and bustle ring 46, at a rate controlled by valve 146, to prevent the uncontrolled entrance of air into the rich gas recycle retort system.

The contact time required for substantially complete eduction in my recycle gas retort can be as low as 10 minutes or less, and generally does not exceed 6 hours. Contact times of about from 1/2 hour to about 3 hours are normal. The longer contact times are required Where the eduction temperatures are in the lower part of the preferred range and the shale particles are relatively large. In the practice of the invention as described above, the shale is usually crushed to particles between about 0 and about 6 inches, preferably of a size which passes a Z-inch mesh sieve and is retained on a 1s-inch mesh sieve. However, either larger or smaller sizes can be used. A particular feature of my recycle gas retort process is the ease with which iines in the range of O to 1/2 inch in size can be retorted. Since there are no high temperature zones in the kiln, the fines do not cause problems in either oVer-retorting of the shale particles or in inducing sintering, fusion or agglomeration, as with retorts having combustion zones.

A particular-embodiment of the present invention has been hereinabove described in considerable detail by Way of illustration. It should be understood that various other modifications and adaptations thereof may be made by those skilled in this particular art without departing from the spirit and scope of this invention as set forth in the appended claims.

I claim: 1. A process for retorting mineral carbonate-containing oil shale which comprises:

passing said shale upwardly in the form of a dense bed from a solids feeder zone successively through a duid-solid disengaging zone, a solids preheating and product cooling zone, and an eduction zone;

passing an essentially oxygen-free hot eduction gas consisting essentially of shale gas downwardly through said eduction Zone at a temperature sufficient to educt shale oil and shale gas from said shale, said .shale in said eduction zone being maintained at a temperature below that at which said mineral carbonates undergo substantial decomposition;

cooling and partially condensing said oil and said gas in said solids preheating and product condensing zone;

removing a gas phase and liquid oil phase from .said

disengaging Zone;

separating said liquid oil phase from said gas phase;

indirectly heating a portion of said gas phase to eduction temperatures;

recycling said heated portion of said gas phase to said eduction Zone as said hot eduction gas to contact said shale therein countercurrently; and

removing spent shale solids from the top of said eduction zone.

2. A process for retorting mineral carbonate-containing oil shale with only minor decomposition of ysaid mineral carbonate, which process comprises:

passing raw shale particles of sizes up to about six inches mean diameter upwardly as a substantially compact bed through an eduction zone;

passing an essentially oxygen-free hot eduction uid consisting essentially of gaseous shale product downwardly through said eduction zone to contact said shale particles thereby educting liquid and gaseous hydrocarbons therefrom, said particles in said eduction zone being maintained at a temperature below that at which said mineral carbonates undergo substantial decomposition;

withdrawing liquid and gaseous shale products from below said eduction zone;

removing educted shale particles from the upper surface of said eduction zone; Y

separating said liquid product from said gaseous product; indirectly heating a portion of said gaseous product to an eduction temperature; and

passing said heated gaseous product to said eduction zone as said hot eduction uid.

3. A process as defined in claim 2 wherein the mean diameter of said shale particles is between about oneeighth inch and about two inches.

4. A process as defined in claim 2 wherein said heated portion of gaseous product passed to the eduction zone is at a temperature between about 1,000 F. and about 1,300 F., and said shale particles in said eduction zone are maintained at a temperature no greater than Yabout 950 F.

5. A process as dened in claim 2 wherein said heated portion of gaseous product is provided to said eduction zone at a rate between about and about 800 pounds per hour per square foot of eduction zone top surface, said shale having a Fischer assay range of between about 10 and about 80 gallons of shale oil per ton of raw shale.

6. In a process wherein (l) mineral carbonate-containing oil shale solids are passed upwardly and successively through a disengaging zone, a solids preheating zone and an eduction zone, (2) a hot eduction gas consisting essentially of product shale gas is simultaneously introduced into the top of said eduction Zone and is passed downwardly and successively through said eduction zone, said solids preheating Zone and said disengaging zone in direct contact with said solids, thereby educting hydrocarbon products from the said solids therein, (3) solids passing through said preheating zone are preheated by heat exchange against said hydrocarbon products and .said eduction gas, (4) said hydrocarbon products and said eduction gas are separated from the said solids in said disengaging zone, (5) the said separated hydrocarbon products and eduction gas are withdrawn from said disengaging zone and introduced into a separation zone wherein the product shale gas phase is Separated from the liquid phase, and (6) spent solids are withdrawn from the top of said eduction zone and are passed downwardly through a spent solids cooling Zone; the improvement which comprises withdrawing said product shale gas phase from said separation zone, heating a first portion of said separated gas phase by indirect heat exchange to form a first hot recycle gas, introducing a second portion of said separated gas phase into said spent solids cooling zone and passing said second portion therethrough in direct contact with the spent solids therein, whereby said second portion is heated by heat exchange against said spent solids to form a second hot recycle gas, and introducing said first and second hot recycle gases into the top of said eduction zone as .said hot eduction gas, said solids in said eduction zone being maintained at a temperature below that at which said mineral carbonates undergo substantial decomposition.

7. A process as defined in claim 6 wherein the mean diameter of said shale particles is between about oneeighth inch and about two inches.

8. A process as defined in claim 6 wherein the mixture of said first and second hot recycle gases is passed to the 9 eduction zone at a temperature between about 1,000 F. and about 1,300 F., and said shale particles in said eduction zone are maintained at a temperature no greater than about 950 F.

9. A process as defined in claim 6 wherein the mixture of said rst and second hot recycle gases is supplied to said eduction zone at a rate between about 100 and about 800 pounds per hour per square foot of eduction zone top surface, said shale having a Fischer assay range of between about lO and about 80 gallons of shale oil per ton of raw shale.

10. A process as defined in claim 6 wherein a third portion of said separated gas phase is combined with the first and second hot recycle gases, and the resulting gas mixture is introduced into the top of said eduction zone as said hot eduction gas.

11. In a process wherein (1) mineral carbonate-containing oil shale solids are passed upwardly and successively through a disengaging zone, a solids preheating zone and an eduction zone, (2) a hot eduction gas consisting essentially of product shale gas is simultaneously introduced into the top of said eduction zone and is passed downwardly and successively through said eduction zone, said solids preheating zone and said disengaging Zone being in direct contact with said solids, (3) within said eduction zone said hot eduction gas educts hydro carbon products from the 4said solids therein, (4) within said solids preheating zone the said solids therein are preheated by heat exchange against said hydrocarbon products and said eduction gas, (5) within said disengaging zone the said hydrocarbon products and said eduction gas are separated from the said solids therein, (6) the said separated hydrocarbon products and eduction gas are withdrawn from said disengaging zone and introduced into a separation zone wherein the product shale gas phase is separated from the liquid phase, and (7) spent solids are withdrawn from the top of said eduction zone and are passed downwardly through a spent solids cooling zone; the improvement which consists in withdrawing said product shale gas phase from said separation Zone, introducing a first portion of said gas phase into a cornbustion zone and therein burning said rst portion in the presence of an oxygen-containing gas and out of contact with said solids and said separated liquid phase to form therein a hot ue gas, heating a second portion of said separated gas phase by indirect heat exchange against said hot iiue gas to form a first hot recycle gas, introducing a third portion of said separated gas phase into said spent solids cooling zone and passing said second portion upwardly therethrough in direct countercurrent contact with the spent solids therein, whereby said third portion is heated by heat exchange against said spent solids t0 form a second hot recycle gas, introducing said first and second hot recycle gases into the top of said eduction zone as said hot eduction gas, and controlling the iiow rates of said rst and second recycle gases so as to maintain an eduction temperature within said eduction zone which is below a temperature at which said mineral carbonates undergo substantial decomposition.

FOREIGN PATENTS 1/1955 Great Britain.

MORRIS O. WOLK, Primary Examiner.

H. A. BIRENBAUM, R, E. SERWIN,

Assistant Examiners. 

1. A PROCESS FOR RETORTING MINERAL CARBONATE-CONTAINING OIL SHALE WHICH COMPRISES: PASSING SAID SHALE UPWARDLY IN THE FORM OF A DENSE BED FROM A SOLIDS FEEDER ZONE SUCCESSIVELY THROUGH A FLUID-SOLID DISENGAGING ZONE, A SOLIDS PREHEATING AND PRODUCT COOLING ZONE, AND AN EDUCTION ZONE; PASSING AN ESSENTIALLY OXYGEN-FREE HOT EDUCTION GAS CONSISTING ESSENTIALLY OF SHALE GAS DOWNWARDLY THROUGH SAID EDUCTION ZONE AT A TEMPERATURE SUFFICIENT TO EDUCT SHALE OIL AND SHALE GAS FROM SAID SHALE, SAID SHALE IN SAID EDUCTION ZONE BEING MAINTAINED AT A TEMPERATURE BELOW THAT AT WHICFH SSAID MINERAL CARBONATES UNDERGO SUBSTANTIAL DECOMPOSITION; COOLING AND PARTIALLY CONDENSING SAID OIL AND SAID GAS IN SAID SOLIDS PREHEATING AND PRODUCT CONDENSING ZONE; REMOVING A GAS PHASE AND LIQUID OIL PHASE FROM SAID DISENGAGING ZONE; SEPARATING SAID LIQUID OIL PHASE FROM SAAID GAS PHASE; INDIRECTLY HEATING A PORTION OF SAID GAS PHASE TO EDUCTION TEMPERATURES; RCYCLING SAID HEATED PORTION OF SAID GAS PHASE TO SAID EDUCTION ZONE AS SAID HOT EDUCTION GAS TO CONTACT SAID SHALE THEREIN COUNTERCURRENTLY; AND 